Duobinary coding is a signaling scheme often employed in optical networks due to its data rate capabilities with a reduced spectrum. Generally, the coding involves summing each current bit with the most recent previously transmitted bit, and providing three possible signal levels corresponding to three states. One of the interesting characteristics of duobinary signaling is that inter-symbol interference (ISI) is introduced in a controlled manner, where two adjacent bits are correlated to introduce the ISI.
For electrical networks that often employ decision-feedback equalizers (DFE) to address ISI, avoiding large 1st post-cursor DFE subtraction is of interest. One reason is the amount of power consumed by each equalizer tap. However, conventional duobinary signaling techniques often introduce unacceptable delays into the DFE critical feedback path. Thus, the need exists for improved equalization techniques for duobinary signaling that provide improved effectiveness in reducing ISI while maintaining power and space efficiencies.